Quick detection of signaling in a wireless communication system

ABSTRACT

Quick frequency tracking (QFT), quick time tracking (QTT), and non-causal pilot filtering (NCP) are used to detect sporadically transmitted signaling, e.g., paging indicators. For QFT, multiple hypothesized frequency errors are applied to an input signal to obtain multiple rotated signals. The energies of the rotated signals are computed. The hypothesized frequency error with the largest energy is provided as a frequency error estimate. For QTT, coherent accumulation is performed on the input signal for a first set of time offsets, e.g., early, on-time, and late. Interpolation, energy computation, and non-coherent accumulation are then performed to obtain a timing error estimate with higher time resolution. For NCP, pilot symbols are filtered with a non-causal filter to obtain pilot estimates for one antenna for non-STTD and for two antennas for STTD. The frequency and timing error estimates and the pilot estimates are used to detect the signaling.

BACKGROUND

I. Field

The present invention relates to communication, and more particularly totechniques for detecting signaling transmitted sporadically in awireless communication system.

II. Background

A wireless device (e.g., a cellular phone) in a wireless communicationsystem may be designed to operate in one of several modes, such as“active” and “idle”, at any given moment. In the active mode, thewireless device can actively exchange data with one or more basestations in the system, e.g., for a voice or data call. In the idlemode, the wireless device may monitor a paging channel (PCH) formessages applicable to the device. Such messages may include pagemessages that alert the wireless device to the presence of an incomingcall and overhead messages that carry system information and otherinformation for the wireless device.

In the idle mode, the wireless device continues to consume power tosustain circuitry needed to monitor the signals transmitted by the basestations in the system. The wireless device may be portable and poweredby an internal battery. Power consumption by the wireless device in theidle mode decreases the available battery power, which shortens thestandby time between battery recharges and the talk time when a call isplaced or received. Hence, it is highly desirable to minimize powerconsumption in the idle mode to increase battery life.

In one common technique for reducing power consumption in the idle mode,user-specific messages are sent on the paging channel to the wirelessdevice at designated times, if at all. The paging channel may be dividedinto numbered frames. The wireless device may be assigned specificframes on which it may receive user-specific messages. With such apaging channel, the wireless device can enter discontinuous reception(DRX) operation whereby it periodically, rather than continuously,monitors the paging channel for messages. While in DRX operation, thewireless device wakes up from a “sleep” state prior to its assignedframe, enters an “awake” state and processes the paging channel formessages, and reverts back to the sleep state if additionalcommunication is not required. The wireless device powers down as muchcircuitry as possible while in the sleep state to conserve batterypower.

In another common technique for further reducing power consumption inthe idle mode, a paging indicator channel (PICH) is used to indicatewhether or not a page message may be sent on the paging channel for thewireless device. The PICH carries paging indicators that are transmittedas binary On/Off values and may be detected quickly. The wireless deviceis assigned a specific paging indicator prior to each assigned frame onthe PCH. The wireless device detects the assigned paging indicator. Ifthe paging indicator indicates that no message will be sent on thepaging channel for the wireless device, then the device would not needto process the paging channel and may go to sleep immediately.

The wireless device typically needs to perform certain tasks afterwaking up from sleep in order to detect the assigned paging indicators.The clock within the wireless device may have drifted, the wirelessdevice may have moved, and/or the channel conditions may have changedduring sleep. The wireless device typically needs to reacquire thefrequency and timing of the signals transmitted by the base stations andestimate the channel response. The wireless device typically wakes upfor a predetermined warm-up period prior to the assigned pagingindicator in order to perform the necessary tasks and get ready todetect the paging indicators. It is desirable to minimize the warm-upperiod in order to reduce battery power consumption and extend batterylife.

There is therefore a need in the art for techniques to detect pagingindicators in a manner to reduce battery power consumption.

SUMMARY

Techniques for performing quick frequency tracking (QFT), quick timetracking (QTT), and non-causal pilot filtering (NCP) to detect signaling(e.g., paging indicators) transmitted sporadically in a wirelesscommunication system are described herein. These techniques may be usedby a wireless device to (1) reduce warm-up time per awake intervalduring DRX operation in the idle mode, (2) reduce battery powerconsumption and extend battery standby time, and (3) provide improveddetection performance under certain operating scenarios. Thesetechniques may be used for signaling sent from one antenna with notransmit diversity and for signaling sent from two antennas withspace-time transmit diversity (STTD). Any one, any combination, or allthree techniques may be used for signaling detection.

For QFT, multiple hypothesized frequency errors are applied to an inputsignal (e.g., despread pilot symbols or descrambled samples) to obtainmultiple rotated signals. The energies of the rotated signals aredetermined, e.g., by performing coherent accumulation followed by energycomputation. The largest energy among the energies for the rotatedsignals is identified, and the hypothesized frequency error with thelargest energy is provided as a frequency error estimate.

For QTT, coherent accumulation is performed on the input signal for afirst set of time offsets (e.g., early, on-time, and late). Non-coherentaccumulation is performed after coherent accumulation. Interpolation isperformed on the first set of time offsets to obtain a timing errorestimate, which is used for signaling detection. The interpolation maybe linear, parabolic, and so on, and may be performed after coherentaccumulation or after non-coherent accumulation.

For NCP, pilot symbols are filtered with a non-causal filter to obtainpilot estimates for one antenna for non-STTD and for two antennas forSTTD. The pilot estimates are used for signaling detection.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout.

FIG. 1 shows a wireless communication system.

FIG. 2 shows a frame structure in W-CDMA.

FIG. 3 shows a common pilot channel (CPICH) in W-CDMA.

FIG. 4A shows DRX reception of the PICH in W-CDMA.

FIG. 4B shows the format of one frame for the PICH.

FIG. 4C shows transmission of the PICH for non-STTD and STTD.

FIG. 5 shows a block diagram of a base station and a wireless device.

FIG. 6 shows a block diagram of a rake receiver within the wirelessdevice.

FIG. 7 shows plots of sinc² functions versus frequency error.

FIGS. 8A and 8B show QFT units for non-STTD and STTD, respectively.

FIG. 9 shows descrambled samples at two times chip rate (or chip×2).

FIG. 10 shows a QTT unit for non-STTD.

FIGS. 11A, 11B and 11C show different embodiments of performing NCP fornon-STTD and STTD.

FIGS. 12A and 12B show data demodulators for non-STTD and STTD,respectively.

FIG. 13 shows a PICH detection process with QFT, QTT, and NCP.

FIG. 14 shows a process for performing QFT during DRX operation.

FIG. 15 shows a process for performing QTT during DRX operation.

FIG. 16 shows a process for performing NCP during DRX operation.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

FIG. 1 shows a wireless communication system 100 with multiple basestations 110 and multiple wireless devices 120. A base station isgenerally a fixed station that communicates with the wireless devicesand may also be called a Node B, a base transceiver subsystem (BTS), anaccess point, or some other terminology. Wireless devices 120 may bedispersed throughout the system. A wireless device may be fixed ormobile and may also be called a mobile station, a user equipment, aterminal, a subscriber unit, or some other terminology. A wirelessdevice may communicate with zero, one, or multiple base stations on thedownlink and/or uplink at any given moment. The downlink (or forwardlink) refers to the communication link from the base stations to thewireless devices, and the uplink (or reverse link) refers to thecommunication link from the wireless devices to the base stations. Awireless device may also be idle and may receive pilot and signalingfrom one or more base stations on the downlink.

The signaling detection techniques described herein may be used forvarious wireless communication systems such as Code Division MultipleAccess (CDMA) systems, Time Division Multiple Access (TDMA) systems,Frequency Division Multiple Access (FDMA) systems, and OrthogonalFrequency Division Multiple Access (OFDMA) systems. A CDMA system mayimplement a radio access technology (RAT) such as Wideband CDMA(W-CDMA), cdma2000, and so on. RAT refers to the technology used forover-the-air communication. A TDMA system may implement a RAT such asGlobal System for Mobile Communications (GSM). Universal MobileTelecommunication System (UMTS) is a system that uses W-CDMA and GSM asRATs and is described in documents from a consortium named “3rdGeneration Partnership Project” (3GPP). cdma2000 is described indocuments from a consortium named “3rd Generation Partnership Project 2”(3GPP2). 3GPP and 3GPP2 documents are publicly available. For clarity,the signaling detection techniques are specifically described below fora W-CDMA system.

FIG. 2 shows a frame structure in W-CDMA. The transmission time line ispartitioned into frames. Each frame has a duration of 10 millisecond(ms) and is divided into 15 slots that are assigned indices of 0 through14. Each slot has a duration of 0.667 ms and spans 2560 chips. Each chiphas a duration of T_(c)=0.260 μs.

FIG. 3 shows the common pilot channel (CPICH) in W-CDMA. The CPICHcarries predefined modulation symbols that may be used by the wirelessdevices for frequency and time tracking and channel estimation. TheCPICH may be transmitted from either (1) one antenna for no transmitdiversity, i.e., non-STTD, or (2) two antennas for STTD. For non-STTD,the symbol sequence for antenna 1 is transmitted from a single basestation antenna, where each “A” represents a modulation symbol of 1+j.For STTD, two symbol sequences shown in FIG. 3 are transmitted from twobase station antennas. A wireless device receives (1) a sum symbol “S”for each symbol period in which modulation symbols “A” and “A” aretransmitted from the two antennas and (2) a difference symbol “D” foreach symbol period in which modulation symbols “A” and “−A” aretransmitted from the two antennas. The use of the CPICH for signalingdetection is described below.

FIG. 4A shows DRX reception of the PICH in W-CDMA. The PICH istransmitted in 10 ms frames. An idle wireless device is assigned pagingoccasions, which are specific frames in which the wireless device canreceive its paging indicators and page messages. The paging occasionsfor the wireless device are separated by a time interval called a DRXcycle. The DRX cycle is configurable for the wireless device and canrange from 80 ms to 5.12 seconds, or from 8 frames to 512 frames. TheDRX cycles and frames for W-CDMA correspond to slot cycles and slots,respectively, in cdma2000.

FIG. 4B shows the format of one frame for the PICH. Each PICH frameincludes 300 bits that are labeled as bits b₀ through b₂₉₉. The first288 bits are used for N_(pi) paging indicators (PIs), and the last 12bits are reserved for other uses. The number of paging indicators(N_(pi)) in each PICH frame is configurable by the system and can takeon a value of 18, 36, 72 or 144. Each paging indicator is sent inN_(b)=288/N_(pi) consecutive bits in the PICH frame, where N_(b) cantake on a value of 16, 8, 4 or 2. The N_(b) bits for each pagingindicator are set to ‘1’ if the paging indicator is equal to ‘1’ and areset to ‘0’ if the paging indicator is equal to ‘0’. The N_(pi) pagingindicators are sent in N_(pi) PI locations that are numbered from 0through N_(pi)−1 (not shown in FIG. 4B).

FIG. 4C shows transmission of the PICH for non-STTD and STTD. For eachPICH frame, the 300 real-valued bits b₀ through b₂₉₉ are used to form150 complex-valued symbols s₀ through s₁₄₉ as follows: s₀=b₀+jb₁,s₁=b₂+jb₃, and so on, and s₁₄₉=b₂₉₈+jb₂₉₉. For non-STTD, the 150 symbolsare transmitted from antenna 1 as shown in FIG. 4C, with each symbolspanning 66.67 μs. For STTD, the 150 symbols are transmitted from bothantennas 1 and 2, with the symbols for antenna 2 being reordered intime, conjugated (“*”), and possibly inverted, as shown in FIG. 4C.

An idle wireless device is associated with a paging indicator in eachpaging occasion. The paging indicator is sent at a PI location that isdetermined by a hash function and can change among the N_(pi) possiblePI locations from paging occasion to paging occasion, as shown in FIG.4A. If the paging indicator for the wireless device is set to ‘1’, thenthe device processes a secondary common control physical channel(S-CCPCH) to check for messages sent for the wireless device. TheS-CCPCH carries the paging channel (PCH), which is a transport channelat a higher layer.

FIG. 5 shows a block diagram of a base station 110 and a wireless device120. At base station 110, an encoder 510 receives traffic data (e.g.,for voice and packet data) and overhead data (e.g., for page and othermessages) from a controller 520. Encoder 510 processes (e.g., encodes,interleaves, and symbol maps) the different types of data and generatesmodulation symbols. A modulator 512 receives the modulation symbols fordata and signaling (e.g., paging indicators), performs channelizationand scrambling on the modulation symbols and signaling for variousphysical channels (e.g., the PICH, CPICH, S-CCPCH, and so on), andprovides a stream of data chips for each antenna. A transmitter unit(TMTR) 514 conditions (e.g., converts to analog, amplifies, filters, andfrequency upconverts) each data chip stream to generate a correspondingdownlink signal, which is transmitted from an associated antenna 516.

At wireless device 120, an antenna 552 receives the downlink signal(s)from base station 110 and provides a received signal to a receiver unit(RCVR) 554. Receiver unit 554 conditions (e.g., filters, amplifies, andfrequency downconverts) the received signal, digitizes the conditionedsignal, and provides input samples. A demodulator (Demod) 560 processesthe input samples and provides symbol estimates. Demodulator 560 furtherperforms detection for paging indicators as described below. A decoder562 processes (e.g., symbol demaps, deinterleaves, and decodes) thesymbol estimates and provides decoded data.

Controllers 520 and 570 direct the operation at base station 110 andwireless device 120, respectively. Memory units 522 and 572 store dataand program codes for controllers 520 and 570, respectively. A timer 574provides time information, which is used by controller 570 to determinewhen to wake up to process the PICH during DRX operation.

FIG. 6 shows a block diagram of a rake receiver 560 a, which is oneembodiment of demodulator 560 in FIG. 5. Rake receiver 560 a includes asearcher 608, R finger processors 610 a through 610 r, where R>1, and asymbol combiner 640. Searcher 608 searches for strong signal instances(or multipaths) in the received signal and provides the strength andtiming of each found multipath that meets a set of criteria. The searchprocessing is known in the art and not described herein.

Each finger processor 610 may be assigned to process a differentmultipath of interest (e.g., a multipath of sufficient strength). Withineach finger processor 610, a sampling unit 612 receives the inputsamples from receiver unit 554 and provides output samples at the propertiming based on a timing error estimate from a time tracking unit 632.For example, sampling unit 612 may receive input samples at eight timesthe chip rate (or chip×8) and may provide output samples at two timesthe chip rate (or chip×2), as shown in FIG. 9. The timing of the on-time(OT) output samples may be selected from one of eight possible timeoffsets for chip×8 based on the timing error estimate. As anotherexample, sampling unit 612 may perform resampling on the input samplesbased on the timing error estimate to generate the output samples. Arotator 614 performs phase rotation on the output samples from samplingunit 612 based on a frequency error estimate from a frequency trackingunit 636 and provides rotated samples. The timing and frequency errorestimates are derived during a warm-up period after waking up fromsleep, as described below. A time tracking loop (TTL) and a frequencytracking loop (FTL) are initialized with the timing and frequency errorestimates, respectively, and are enabled during the detection of apaging indicator. A descrambler 616 multiplies the rotated samples witha descrambling sequence for a base station being received and providesdescrambled samples R_(i).

To recover the pilot from the CPICH, a pilot despreader 618 multipliesthe descrambled samples with a pilot channelization code, C_(pilot), andfurther accumulates N_(p) resultant samples to obtain a pilot symbolP_(n), which may also be called a received pilot symbol or a despreadpilot symbol. The channelization codes are OVSF codes in W-CDMA. N_(p)is the length of the pilot channelization code, which is 256 chips forW-CDMA. A pilot filter 620 filters the pilot symbols and provides pilotestimates {circumflex over (P)}_(n) for the CPICH.

To detect a paging indicator on the PICH, a data despreader 622multiplies the descrambled samples with a channelization code for thePICH, C_(pich), accumulates the resultant samples over the length of thePICH channelization code (which is 256 chips for W-CDMA), and provides adata symbol D_(n). A data demodulator 624 performs detection on the datasymbols with the pilot estimates and provides symbol estimates. Symbolcombiner 640 receives and combines the symbol estimates from allassigned finger processors and provides final symbol estimates. Thepertinent blocks within rake receiver 560 a are described below.

During DRX operation in the idle mode, wireless device 120 is requiredto monitor the PCH and respond back to the base station if there is apage for the wireless device. To accomplish this, the wireless devicewakes up at regular intervals based on its DRX cycle, as shown in FIG.4A, and detects the paging indicator on the PICH to determine if a pagemessage might be sent on the S-CCPCH for the wireless device in thefollowing S-CCPCH frame. To reliably detect the paging indicator, thewireless device typically performs frequency tracking to estimate andtrack out frequency error, time tracking to estimate and track outtiming error, and pilot filtering to obtain pilot estimates ofsufficient quality. Frequency and time tracking are performed to keepthe searcher and finger processors latched to the current channelconditions.

The wireless device may perform frequency tracking, time tracking, andpilot filtering using various techniques. The radio frequency (RF)circuitry within receiver unit 554 is typically turned on for theduration of these tasks. The amount of time needed to perform thesetasks is dependent on the specific techniques used for the tasks and mayaccount for a significant fraction of the total RF awake time for eachawake interval. The RF awake time has a large impact on battery powerconsumption in the idle mode. A longer RF awake duration for each awakeinterval results in higher power consumption and hence shorter batterystandby time. Battery standby time has a large impact on acceptabilityand commercial success of the wireless device. Thus, it is highlydesirable to perform these tasks in the shortest amount of timepossible.

Table 1 lists three techniques that may be used for frequency tracking,time tracking, and pilot filtering. TABLE 1 Technique Description Quickfrequency tracking Open-loop technique for estimating frequency (QFT)error. Quick time tracking Open-loop technique for estimating timing(QTT) error. Non-causal pilot filtering Use of a non-causal finiteimpulse response (NCP) (FIR) filter to derive high quality pilotestimates.QFT, QTT, and NCP may be performed on descrambled samples fromdescrambler 616 or pilot symbols from pilot despreader 618. For clarity,QFT, QTT, and NCP based on pilot symbols are described below. In thefollowing description, coherent accumulation refers to accumulation ofcomplex values, and the phases of the complex values affect theaccumulation result. Non-coherent accumulation refers to accumulation ofreal values, e.g., energies.

1. Quick Frequency Tracking (QFT)

QFT is an open-loop frequency estimation technique that can provide afrequency error estimate in a fixed amount time regardless of the amountof frequency error and the channel conditions. This is in contrast to aclosed-loop frequency estimation technique that requires longer time fora larger frequency error and/or poor channel conditions. QFT may be usedto provide a quick one-shot frequency error estimate at each awakeinterval. For QFT, the pilot symbols are rotated with differenthypothesized frequency errors, the pilot energy is computed for eachhypothesized frequency error, and the hypothesized frequency error withthe largest pilot energy is provided as the frequency error estimate.

A complex-valued pilot symbol from pilot despreader 618 may be expressedas: $\begin{matrix}\begin{matrix}{P_{n} = {P_{I,n} + {j\quad P_{Q,n}}}} \\{= {\left( {{{S_{p} \cdot \sin}\quad{{c\left( {\Delta\quad{f \cdot T_{p}}} \right)} \cdot \cos}\quad\theta} + {S_{w} \cdot w_{I}^{p}}} \right) + {j\left( {S_{\quad p} \cdot} \right.}}} \\\left. {{\sin\quad{{c\left( {\Delta\quad{f \cdot T_{\quad p}}} \right)} \cdot \sin}\quad\theta} + {S_{w} \cdot w_{Q}^{p}}} \right)\end{matrix} & {{Eq}\quad(1)}\end{matrix}$where

-   -   P_(n), is the pilot symbol for pilot symbol period n;    -   P_(I,n), and P_(Q,n) are inphase (I) and quadrature (Q) pilot        components, respectively;    -   S_(p)=N_(p)·√{square root over (2E_(c)/I_(o))} and        S_(w)=√{square root over (N_(p))}·√{square root over        (2N_(t)/I_(o))};    -   E_(c)/I_(o) is the pilot energy-per-chip-to-total-noise ratio;    -   N_(t)=I_(o)−I_(or) is the total noise minus noise on the pilot        scrambling code;    -   Δf is the actual frequency error in the pilot symbol;    -   T_(p)=N_(p)·T_(c) is the duration of one pilot symbol;    -   θ is the phase of the pilot symbol; and    -   w_(l) ^(P) and w_(Q) ^(p) are Gaussian noise for the I and Q        pilot components, respectively, with zero mean and unit        variance.        The phase term θ may be expressed as:        θ=2π·Δf·N _(p) ·T _(c)+φ=Φ+φ,  Eq (2)        where

φ is the random phase of the pilot symbol; and

Φ is the phase shift per pilot symbol period caused by the frequencyerror Δf

Equation (1) indicates that coherent accumulation of the descrambledsamples by pilot despreader 618 in the presence of frequency error Δfresults in the sinc (Δf·T_(p)) term appearing in both the I and Q pilotcomponents. This sinc (Δf·T_(p)) term represents degradation in themagnitude of the I and Q pilot components due to the frequency error.

The pilot symbols may be coherently accumulated, and the pilot energy,E_(p), may be computed as follows: $\begin{matrix}{{E_{p} = {\left\lbrack {\sum\limits_{n = 1}^{N_{fc}}P_{I,n}} \right\rbrack^{2} + \left\lbrack {\sum\limits_{n = 1}^{N_{fc}}P_{Q,n}} \right\rbrack^{2}}},} & {{Eq}\quad(3)}\end{matrix}$where N_(fc) is the coherent accumulation length, in number of pilotsymbols. The pilot energy E_(p) includes a sinc² (Δf·N_(fc)·T_(p)) termthat represents the degradation from peak pilot energy due to thefrequency error Δf.

FIG. 7 shows plots of the degradation term sinc² (Δf·N_(fc)·T_(p)) as afunction of frequency error for different values of N_(fc). Plot 710 isfor a coherent accumulation length of N_(fc)=8 pilot symbols, plot 712is for N_(fc)=16, and plot 714 is for N_(fc)=30. For a given value ofN_(fc), the pilot energy is maximum with no frequency error (Δf=0) anddecreases based on a sinc function as the frequency error increases. Alarger value of N_(fc) corresponds to a more narrow curve for the sinc²(Δf·N_(fc)·T_(p)) term, which allows for easier detection of zero or lowfrequency errors based on the pilot energy since the sinc term drops offmore abruptly for larger frequency errors. A larger N_(fc) value resultsin more distinction among pilot energies for different frequency errors.

FIG. 8A shows a block diagram of an embodiment of a QFT unit 638 a fornon-STTD. QFT unit 638 a may be used for frequency tracking unit 636 forone finger processor 610, as shown in FIG. 6. QFT unit 638 a includes Kpilot processors 810 a through 810 k, where K>1, and a frequency errordetector 820. Each pilot processor 810 performs processing for adifferent hypothesized frequency error.

The pilot symbols from pilot despreader 618 are provided to all K pilotprocessors 810 a through 810 k. Within each processor 810, a multiplier812 multiplies each pilot symbol P_(n) with a phasor S(Δf_(k))=exp(−j2π·Δf_(k)·n·T_(p)) and provides a rotated pilot symbol P_(k,n), whereΔf_(k) is the hypothesized frequency error for that processor 810. Therotation of the pilot symbols by the hypothesized frequency error Δf_(k)results in the frequency error for the rotated pilot symbols becomingΔf−Δf_(k) and the sinc term in equation (1) becoming sinc((Δf−Δf_(k))·T_(p)) after the rotation. A coherent accumulator 814accumulates N_(fc) rotated pilot symbols, as follows: $\begin{matrix}{{{P_{I,k,{acc}} = {\sum\limits_{n = 1}^{N_{fc}}P_{I,k,n}}},\quad{and}}{{P_{Q,k,{acc}} = {\sum\limits_{n = 1}^{N_{fc}}P_{Q,k,n}}},}} & {{Eq}\quad(4)}\end{matrix}$where P_(k,n)=P_(I,k,n)+jP_(Q,k,n). The coherent accumulation lengthN_(fc) may be a fixed value or a configurable value that is determinedbased on expected channel conditions. An energy computation unit 816computes the pilot energy as follows:E _(k) =P _(I,k,acc) ² +P _(Q,k,acc) ².  Eq (5)

Because of the rotation by exp(−j2π·Δf_(k)·n·T_(p)), the degradationterm for the pilot energy becomes sinc² ((Δf−Δf_(k))·N_(fc)·T_(p)). Thedegradation in the pilot energy due to frequency error reduces as thehypothesized frequency error Δf_(k) approaches the actual frequencyerror Δf. Frequency error detector 820 receives the pilot energies fromall K pilot processors 810 a through 810 k and identifies the largestpilot energy. Detector 820 then provides the hypothesized frequencyerror Δf_(k,max) corresponding to the largest pilot energy, which is thehypothesis that is closest to the actual frequency error, as thefrequency error estimate, or Δ{circumflex over (f)}=Δf_(k,max).

FIG. 8B shows a block diagram of an embodiment of a QFT unit 638 b forSTTD. QFT unit 638 b includes K pilot processors 850 a through 850 k anda frequency error detector 860. Each pilot processor 850 performsprocessing for a different hypothesized frequency error. The pilotsymbols are provided to all K pilot processors 850 a through 850 k.Within each processor 850, a multiplier 852 multiplies each pilot symbolP_(n) with a phasor S(Δf_(k)) and provides a rotated pilot symbol. Therotated pilot symbols from multiplier 852 are provided to two coherentaccumulators 854 x and 854 y for two base station antennas. Accumulator854 x accumulates N_(fc) rotated pilot symbols as shown in equation set(4). Accumulator 854 y accumulates N_(fc) rotated pilot symbols asfollows: $\begin{matrix}{{{P_{2,I,k,{acc}} = {\sum\limits_{n = 1}^{N_{fc}}{P_{I,k,n} \cdot K_{n}}}},\quad{and}}{{P_{2,Q,k,{acc}} = {\sum\limits_{n = 1}^{N_{fc}}{P_{Q,k,n} \cdot K_{n}}}},}} & {{Eq}\quad(6)}\end{matrix}$where K_(n) is a gain that is equal to +1 for “S” pilot symbols and −1for “D” pilot symbols in FIG. 3. Equation set (6) performs both STTDdecoding for the CPICH and coherent accumulation. The coherentaccumulation period N_(fc) is an even number of pilot symbols for STTD.

Energy computation units 856 x and 856 y compute the pilot energies forthe outputs of accumulators 854 x and 854 y, respectively, as shown inequation (5). A combiner 858 sums the pilot energies from units 856 xand 856 y and provides an overall pilot energy for the hypothesizedfrequency error. A frequency error detector 860 receives the overallpilot energies for all K hypothesized frequency errors and provides thehypothesized frequency error corresponding to the largest overall pilotenergy as the frequency error estimate.

The complexity and processing time for QFT are dependent on threeparameters: the coherent accumulation length (N_(fc)), the number offrequency error hypotheses (K), and the range of hypothesized frequencyerrors. The frequency error range is determined by the expectedworst-case frequency drift (e.g., due to Doppler and temperature change)from one awake interval to the next awake interval. The frequency errorrange may be determined based on the DRX cycle, the oscillator design,and so on. A larger frequency error range may be assumed for a longerDRX cycle, and vice versa. The number of hypotheses (K) may be selectedbased on the frequency error range, the desired precision for thefrequency error estimate, and the amount of time to allocate for QFT. Ingeneral, greater precision and smaller standard deviation in thefrequency error estimate may be obtained with more hypotheses. The Khypotheses may be distributed (1) uniformly across the entire frequencyerror range or (2) non-uniformly with smaller frequency error spacingbeing used in any subrange with a higher likelihood of containing theactual frequency error. A longer accumulation length can reduce both thepeak residual frequency error and the standard deviation of the residualerror for (1) an AWGN channel and (2) a Rayleigh fading channel at lowspeeds. The residual frequency error is the difference between theactual frequency error and the frequency error estimate, orΔf_(res)=Δf−Δ{circumflex over (f)}.

FIGS. 8A and 8B show derivation of the frequency error estimate for onefinger processor. Multiple finger processors may be assigned to processmultiple signal instances or multipaths. A common frequency errorestimate may be computed for all assigned finger processors in variousmanners.

In one embodiment, the frequency error estimate is determined for eachassigned finger processor as shown in FIG. 8A. The common frequencyerror estimate may then be computed based on the frequency errorestimates for all assigned finger processors, as follows:$\begin{matrix}{{{\Delta\quad f_{com}} = {\sum\limits_{r = 1}^{R}{\Delta\quad{{\hat{f}}_{r} \cdot C_{r}}}}},} & {{Eq}\quad(7)}\end{matrix}$where

-   -   Δ{circumflex over (f)}_(r) is the frequency error estimate for        finger processor r;    -   C_(r) is a weight for finger processor r; and    -   Δf_(com) is the common frequency error estimate for all assigned        finger processors.        The weight C_(r) for each finger processor may be equal to        E_(c)/I_(o) or some other quality metric for that finger        processor.

In another embodiment, the pilot energies are first accumulated acrossall assigned finger processors for each hypothesized frequency error, asfollows: $\begin{matrix}{{E_{k,\quad{total}} = {\sum\limits_{r = 1}^{R}E_{r,k}}},} & {{Eq}\quad(8)}\end{matrix}$where

-   -   E_(r,k) is the pilot energy for finger processor r for        hypothesized frequency error Δf_(k); and    -   E_(k,total) is the total pilot energy for all assigned finger        processors with Δf_(k).        The hypothesized frequency error corresponding to the largest        total pilot energy is then provided as the common frequency        error estimate.

Frequency tracking may be performed in various manners. In anembodiment, the common frequency error estimate is applied to anoscillator that determines the frequency of a local oscillator (LO)signal used for frequency downconversion. Each finger processor performsfrequency tracking based on the residual frequency error determined forthat finger processor. In another embodiment, each finger processorperforms frequency tracking based on the frequency error estimatederived for that finger processor. In yet another embodiment, frequencytracking is performed across all finger processors based on the commonfrequency error estimate.

2. Quick Time Tracking (OTT)

QTT is an open-loop timing estimation technique that can provide atiming error estimate in a fixed amount time regardless of the amount oftiming error and the channel conditions. This is in contrast to aclosed-loop timing estimation technique that requires longer time for alarger timing error and/or poor channel conditions. QTT may be used toprovide a quick one-shot timing error estimate at each awake interval.

FIG. 9 shows descrambled samples at chip×2 for one finger processor 610.For each chip period i, the on-time (OT) sample is the descrambledsample at that chip timing, the early (E) sample is the descrambledsample ½ chip earlier, and the late (L) sample is the descrambled sample½ chip later. The early, on-time, and late samples are thus ½ chipapart. The late sample for chip period i is also the early sample forchip period i+1.

Descrambler 616 may provide descrambled samples at chip×2. Pilotdespreader 618 may perform despreading on the chip×2 descrambled samplesand provide early (E), on-time (OT), and late (L) pilot symbols. Foreach pilot symbol period, pilot despreader 618 may accumulate N_(p)on-time samples to obtain an on-time pilot symbol, N_(p) early samplesto obtain an early pilot symbol, and N_(p) late samples to obtain a latepilot symbol. The early, on-time, and late pilot symbols are ½ chipapart and may be used to estimate timing error.

FIG. 10 shows a block diagram of an embodiment of a QTT unit 634 a fornon-STTD. QTT unit 634 a may be used for time tracking unit 632 for onefinger processor 610, as shown in FIG. 6. Within QTT unit 634 a, ademultiplexer 1012 receives the early, on-time, and late pilot symbolsfrom pilot despreader 618, provides early pilot symbols to a coherentaccumulator 1014 a, provides on-time pilot symbols to a coherentaccumulator 1014 b, and provides late pilot symbols to a coherentaccumulator 1014 c. Each accumulator 1014 accumulates its pilot symbolsover a coherent accumulation length N_(tc) and provides a pilot valuefor that period. An interpolator 1016 receives an early pilot valueY_(E), an on-time value Y_(OT), and a late pilot value Y_(L) fromaccumulators 1014 a, 1014 b, and 1014 c, respectively, for each coherentaccumulation period. In an embodiment, interpolator 1016 performs linearinterpolation on the early, on-time, and late pilot values, as follows:Y _(E+1/8)=(51/64)·Y _(E)+(17/64)·Y _(OT),Y _(OT+3/8)(51/64)·Y _(L)+(17/64)·Y _(OT),Y _(E+1/4)=(35/64)·Y _(E)+(35/64)·Y _(OT),Y _(OT+1/4)=(35/64)·Y _(L)+(35/64)·Y _(OT),Y _(E+3/8)=(17/64)·Y _(E)+(51/64)·Y _(OT),Y _(OT+1/8)=(17/64)·Y _(L)+(51/64)·Y _(OT)  Eq (9)In equation set (9), the weights are selected to provide goodperformance for linear interpolation. Other weights may also be used.

For each coherent accumulation period, interpolator 1016 provides eightpilot values for eight different time offsets of one chip period, orchip×8 time offsets. An energy computation unit 1018 computes the energyof each pilot value received from interpolator 1016 and, for eachcoherent accumulation period, provides eight energy values for the eightdifferent time offsets. A non-coherent accumulator 1020 accumulatesN_(tnc) energy values for each time offset and provides an accumulatedenergy value for that time offset. A timing error detector 1022 receiveseight accumulated energy values for the eight time offsets, identifiesthe largest accumulated energy value, determines the time offsetcorresponding to the largest accumulated energy value, and provides thedifference between this time offset and the on-time position as thetiming error estimate.

In another embodiment, the QTT unit performs parabolic interpolation toobtain the timing error estimate. For this embodiment, the energy ofeach pilot value from accumulators 1014 a, 1014 b, and 1014 c iscomputed. N_(tnc) energy values for early pilot symbols are accumulatedto obtain an early energy value E_(E), N_(tnc) energy values for on-timepilot symbols are accumulated to obtain an on-time energy value E_(OT),and N_(tnc) energy values for late pilot symbols are accumulated toobtain a late energy value E_(L). The timing error estimate is thencomputed as follows: $\begin{matrix}{{\Delta\quad\hat{t}} = {\frac{E_{L} - E_{E}}{{2E_{OT}} - E_{E} - E_{L}}.}} & {{Eq}\quad(10)}\end{matrix}$Parabolic interpolation attempts to fit a parabola through the threepoints E_(E), E_(OT) and E_(L). The peak position of the parabola isprovided as the timing error estimate.

For both linear and parabolic interpolation, the coherent accumulationlength N_(tc) and the non-coherent accumulation length N_(tnc) may beselected to provide the desired performance. QTT may be performed inparallel with QFT. In this case, the descrambled samples and the pilotsymbols will likely have frequency error that has not been tracked out.Hence, the coherent accumulation length should be limited. The totaltime required for QTT may be selected to approximately match the totaltime required for QFT. In this case, the total accumulation length forQTT may be approximately equal to the coherent accumulation length forQFT, or N_(tc)×N_(tnc)≈N_(fc). Various combinations of (N_(tc), N_(tnc))were evaluated for different channel conditions. Combinations of (5, 6)and (3, 10) provide good performance for the tested channel conditions.Other combinations of (N_(tc), N_(tnc)) may also be used, and this iswithin the scope of the invention.

For STTD with linear interpolation, coherent accumulation is performedseparately for the two base station antennas to obtain a set of early,on-time, and late pilot values for each antenna. Linear interpolation isperformed on the early, on-time, and late pilot values for each antennato obtain a set of eight pilot values at eight time offsets for thatantenna. Energies are computed for each of the eight pilot values foreach antenna. The energies of the pilot values for the two antennas arenon-coherently accumulated for each of the eight time offsets. Thetiming error estimate is then obtained based on the time offset of thelargest accumulated energy value.

The pilot values for each antenna may be derived as follows:$\begin{matrix}{{{Y_{1,{tos}} = {\sum\limits_{n = 1}^{N_{fc}}P_{{tos},n}}},\quad{and}}\quad{{Y_{2,{tos}} = {\sum\limits_{n = 1}^{N_{fc}}{P_{{tos},n} \cdot K_{n}}}},}} & {{Eq}\quad(11)}\end{matrix}$where “tos” denotes time offset, which may be early (E), on-time (OT),or late (L);

-   -   P_(tos,n) is the pilot symbol at the designated time offset in        pilot symbol period n;    -   K_(n) is equal to +1 for “S” pilot symbols and −1 for “D” pilot        symbols; and    -   Y_(1,tos) and Y_(2,tos) are pilot values at the designated time        offset for antennas 1 and 2, respectively.        Equation set (11) performs both STTD decoding for the CPICH and        coherent accumulation. For each coherent accumulation period,        equation set (11) provides a first set of pilot values Y_(1,E),        Y_(1,OT) and Y_(1,L) for antenna 1 and a second set of pilot        values Y_(2,E), Y_(2,OT) and Y_(2,L) for antenna 2.

The three pilot values in the first set are interpolated as shown inequation set (9) to obtain a first set of eight pilot values. The threepilot values in the second set are also interpolated to obtain a secondset of eight pilot values. The energies of the eight pilot values ineach set are computed for each antenna. The energies of the eight pilotvalues in the two sets for the two antennas are combined for each timeoffset. Non-coherent accumulation and timing error detection are thenperformed as described above for non-STTD. For STTD, N_(tc) is an evenvalue, and combinations of (4, 7) and (6, 5) provide good performancefor the tested channel conditions.

For both non-STTD and STTD and for both linear and parabolicinterpolation, the coherent accumulation length N_(tc) and thenon-coherent accumulation length N_(tnc) may be selected based on theexpected channel conditions. Shorter accumulation lengths may be usedfor favorable channel conditions so that the time needed to perform QTTcan be reduced.

The description above is for derivation of the timing error estimate forone finger processor. Multiple finger processors may be assigned toprocess multiple signal instances. A timing error estimate may bederived for each finger processor, and the timing of the fingerprocessor is moved based on this timing error estimate prior toperforming detection.

3. Non-Causal Pilot Filtering (NCP)

Non-causal pilot filtering (NCP) provides pilot estimates used fordetection of a paging indicator. The paging indicator (PI) transmissionduring any pilot symbol period is called a PI symbol. The pagingindicator may span 1, 2, 4 or 8 pilot symbol periods and may thuscomprise 1, 2, 4 or 8 PI symbols. NCP provides (1) a pilot estimate foreach PI symbol for non-STTD and (2) two pilot estimates for two basestation antennas for each pair of PI symbols for STTD.

FIG. 11A shows an embodiment of performing NCP for one PI symbol fornon-STTD. L+1 pilot symbols centered around the PI symbol are used toderive a pilot estimate for the PI symbol. The pilot estimate may bederived based on a FIR filter, as follows: $\begin{matrix}{{{\hat{P}}_{n} = {\sum\limits_{\ell = {{- L}/2}}^{L/2}{P_{n + \ell} \cdot W_{\ell}}}},} & {{Eq}\quad(12)}\end{matrix}$where

-   -   W_(t) is the coefficient for the l-th FIR filter tap; and    -   {circumflex over (P)}_(n) is the pilot estimate for PI symbol        period n.        The FIR filter length L+1 and coefficients may be selected to        provide good performance for different channel conditions. FIR        filter lengths of 5, 7 and 9 provide good performance for the        tested channel conditions, but other FIR filter lengths may also        be used. The coefficients may be selected to be all ones, in        which case the pilot estimate is obtained by simply accumulating        L+1 pilot symbols centered around the PI symbol. Other values        may also be used for the coefficients.

For STTD, the paging indicator may be transmitted in 1, 2, or 4 PIsymbol pairs from two antennas. For each PI symbol pair, symbols s_(a)and s_(b) are transmitted from antenna 1 and symbols −s*_(b) and s*_(a)are transmitted from antenna 2, as shown in FIG. 4C.

FIG. 11B shows an embodiment of performing NCP for one PI symbol pairfor STTD. The PI symbol pair may be transmitted starting in any pilotsymbol period. A pilot estimate for each antenna is needed in order toperform STTD decoding of the PI symbol pair. The pilot estimate for eachantenna may be obtained by filtering equal number of “S” and “D” pilotsymbols. Referring back to FIG. 3, the pilot pattern for antenna 2 has adiscontinuity at the CPICH frame boundary so that (1) a single “−A”symbol is transmitted between two “A” symbols at the end of a CPICHframe and (2) a single “A” symbol is transmitted between two “−A”symbols at the start of the CPICH frame. Hence, depending on thestarting position of a PI symbol pair relative to the CPICH frame,different FIR filter lengths may be used to ensure that equal number of“S” and “D” pilot symbols are filtered for the PI symbol pair, as shownin FIG. 11B. The 150 pilot symbol periods in each CPICH frame may begiven indices of 0 through 149. The FIR filter length L may be selectedto be (1) L=2, 6, 10 or some other value if the PI symbol pair starts onan even-index pilot symbol period (not shown in FIG. 11B) and (2) L=4, 8or some other value if the PI symbol pair starts on an odd-index pilotsymbol period (as shown in FIG. 11B).

The pilot estimates for the two antennas may be derived based on FIRfilters, as follows: $\begin{matrix}{{{{\hat{P}}_{1,n} = {\sum\limits_{\ell = {{- L}/2}}^{{L/2} + 1}{P_{n + \ell} \cdot W_{\ell}}}},\quad{and}}{{{\hat{P}}_{2,n} = {\sum\limits_{\ell = {{- L}/2}}^{{L/2} + 1}{P_{n + \ell} \cdot W_{\ell} \cdot K_{n + \ell}}}},}} & {{Eq}\quad(13)}\end{matrix}$where

-   -   K_(n) is equal to +1 for “S” pilot symbols and −1 for “D” pilot        symbols; and    -   {circumflex over (P)}_(1,n) and {circumflex over (P)}_(2,n) are        pilot estimates for antennas 1 and 2, respectively, for the PI        symbol pair starting in PI symbol period n.        The weights W_(l) may be selected to be all ones or some other        values. Equation (13) shows two non-causal FIR filters used for        two antennas. Each non-causal FIR filter is defined by a set of        weights W_(l) and a set of gains K_(n), where the gains are        dependent on the antenna and the symbol period n.

FIG. 11C shows another embodiment of performing NCP for different PIsymbol pairs for STTD. For this embodiment, the 150 pilot symbols ineach CPICH frame are arranged into 75 pilot symbol pairs that aredenoted as pair 1 through pair 75. A given PI symbol pair may be timealigned with a pilot symbol pair or may span across two pilot symbolpairs. For example, PI symbol pair X in FIG. 11C is time aligned withpilot symbol pair 1, and PI symbol pair Y in FIG. 11C spans across pilotsymbol pair 75 in a prior CPICH frame and pilot symbol pair 1 in thecurrent CPICH frame.

If a PI symbol pair is time aligned with a pilot symbol pair, then NCPmay be performed using the pilot symbol pairs surrounding this PI symbolpair to obtain pilot estimates for the two antennas, e.g., as shown inequation (13). For the example shown in FIG. 11C, pilot symbol pairs 74,75, 1, 2, 3 may be used to obtain pilot estimates for PI symbol pair X.The number of pilot symbol pairs used to derive the pilot estimates maybe configurable.

If a PI symbol pair spans two pilot symbol pairs, then NCP may beperformed using various combinations of pilot symbol pairs surroundingthis PI symbol pair. For the example shown in FIG. 11C, the pilotestimates for PI symbol pair Y may be obtained based on any one of thefollowing schemes.

-   -   1. Use pilot symbol pairs 74, 75 and 1 to obtain the pilot        estimates for the two antennas as shown in equation (13).    -   2. Use pilot symbol pairs 75, 1 and 2 to obtain the pilot        estimates for the two antennas as shown in equation (13).    -   3. Use pilot symbol pairs 74, 75 and 1 to obtain two sets of        pilot estimate(s) for the two antennas, use pilot symbol pairs        75, 1 and 2 to obtain another two sets of pilot estimate(s) for        the two antennas, and jointly use these four sets of pilot        estimate(s) for the two antennas to perform STTD decoding of the        PI symbol pair.    -   4. Use pilot symbol pairs 74, 75 and 1 to obtain two set of        pilot estimate(s) for the two antennas, use pilot symbol pairs        75, 1 and 2 to obtain another two sets of pilot estimate(s) for        the two antennas, average the two sets of pilot estimate(s) for        each antenna to obtain a set of averaged pilot estimate(s) for        that antenna, and use the two sets of averaged pilot estimate(s)        for the two antennas to perform STTD decoding of the PI symbol        pair.

For cases 1 and 2 above, the non-causal FIR filters for the two antennasare non-symmetric about the PI symbol pair and operate on unequalnumbers of pilot symbols on the left and right sides of the PI symbolpair. For example, if pilot symbol pairs 74, 75 and 1 are used, thenthere are two pilot symbol pairs 74 and 75 on the left side of the PIsymbol pair and one pilot symbol pair 1 on the right side of the PIsymbol pair.

For cases 3 and 4 above, two non-causal FIR filters operate on a firstset of pilot symbols (e.g., pilot symbol pairs 74, 75 and 1) to generatetwo sets of pilot estimate(s) for the two antennas, and another twonon-causal FIR filters operate on a second set of pilot symbols (e.g.,pilot symbol pairs 75, 1 and 2) to generate another two sets of pilotestimate(s) for the two antennas. Four sets of pilot estimate(s) areobtained for the two antennas, where each set contains one or more pilotestimates. The two sets of pilot estimate(s) for each antenna may beaveraged, and the two sets of averaged pilot estimate(s) may be used forSTTD decoding, as described below. Alternatively, the four sets of pilotestimate(s) for the two antennas may be used for joint STTD decoding, asalso described below.

4. Paging Indicator Detection

FIG. 12A shows a block diagram of an embodiment of a data demodulator624 a for non-STTD. NCP pilot filter 620 filters the pilot symbols P_(n)with a non-causal FIR filter and provides a pilot estimate {circumflexover (P)}_(n) for each PI symbol. Within demodulator 624 a, a phaserotator 1212 multiplies each pilot estimate with 1−j1 and provides acorresponding channel gain estimate H_(n). The multiplication with 1−j1rotates the pilot estimate by −45° and removes the pilot modulationsince A=1+j1. A multiplier 1214 receives the PI symbols from datadespreader 622 and the channel gain estimates from rotator 1212.Multiplier 1214 multiplies each PI symbol with the associated channelgain estimate and provides a complex-value demodulated symbol. Each biton the PICH is transmitted on either the I or Q component of a QPSKmodulation symbol. A combiner 1216 sums the real and imaginary parts ofeach demodulated symbol and provides a detected paging indicator valuefor the corresponding PI symbol.

Symbol combiner 640 receives and combines the detected values from allassigned finger processors for each PI symbol. Symbol combiner 640 alsoaccumulates the detected values over all PI symbols for the pagingindicator and provides a final detected value for the paging indicator.The final detected value may be compared against a predeterminedthreshold to determine whether the transmitted paging indicator was setto ‘1’or ‘0’.

FIG. 12B shows a block diagram of an embodiment of a data demodulator624 b for STTD. NCP pilot filter 620 filters the pilot symbols P_(n)with non-causal FIR filters and provides pilot estimates {circumflexover (P)}_(1,n) and {circumflex over (P)}_(2,n) for antennas 1 and 2,respectively, for each PI symbol pair. Within demodulator 624 b, a phaserotator 1252 receives the pilot estimates {circumflex over (P)}_(1,n)and {circumflex over (P)}_(2,n) X rotates each pilot estimate by −45°,and provides channel gain estimates H_(1,n) and H_(2,n) for antennas 1and 2, respectively, for each PI symbol pair. An STTD decoder 1254receives the PI symbols from data despreader 622 and the channel gainestimates and performs STTD decoding, as follows:Ŝ _(n) =H* _(1,n) ·D _(n) +H _(2,n) ·D* _(n+1), andS _(n+1) =−H _(2,n) ·D* _(n) +H* _(1,n) ·D _(n+1),  Eq (14)where

-   -   D_(n) and D_(n+1) are PI symbols for PI symbol periods n and        n+1, respectively;    -   Ŝ_(n) and Ŝ_(n+1) are estimates of the transmitted PI symbols        for PI symbol periods n and n+1, respectively; and    -   “*” denotes a complex conjugate.        A combiner 1256 sums the real and imaginary parts of Ŝ_(n) and        Ŝ_(n+1) and provides a detected value for the PI symbol pair.        Symbol combiner 640 combines the detected values from all        assigned finger processors and across all PI symbol pairs for        the paging indicator and provides a final detected value for the        paging indicator.

Joint STTD decoding may be performed in various manners with four setsof pilot estimate(s) for the two antennas. For example, the D_(n) PIsymbol may be multiplied with channel gain estimates obtained from thetwo sets of pilot estimate(s) derived from the first set of pilotsymbols, and the D_(n+1) PI symbol may be multiplied with channel gainestimates obtained from the other two sets of pilot estimate(s) derivedfrom the second set of pilot symbols.

FIG. 13 shows a process 1300 for performing PICH detection with QFT,QTT, and NCP. Prior to going to sleep in the prior awake interval, theamount of time needed to perform frequency tracking in the current awakeinterval is determined based on the expected channel conditions. Thecoherent accumulation length N_(fc) for QFT and the coherent andnon-coherent accumulation lengths N_(tc) and N_(tnc) for QTT may bereduced for favorable channel conditions (e.g., if E_(c)/I_(o) is abovea predetermined threshold) in order to reduce the amount of timeallocated for QFT and QTT. In any case, the wireless device wakes upprior to the paging indicator in the current awake interval by an amountof time determined in the prior awake interval.

For the current awake interval, the wireless device wakes up at thedetermined time and searches for strong signal instances and/orreacquires strong signal instances identified in the prior awakeinterval (block 1310). The common frequency error estimate from theprior awake interval is used for the search/reacquisition in the currentawake interval. The searcher provides the strength and timing (e.g., tochip×2 resolution) of each found signal instance that meets a set ofcriteria. A finger processor is assigned to process each signal instanceof interest.

For frequency tracking, the rotator within each assigned fingerprocessor is set to the common frequency error estimate from the priorawake interval (block 1312). QFT is then performed to obtain a frequencyerror estimate for each finger processor and to update the commonfrequency error estimate for all finger processors (block 1314). Thefrequency error estimate for each finger processor is equal to thefrequency error estimate provided by the QFT for that finger processorminus the common frequency error estimate and is the residual frequencyerror for the finger processor. The oscillator is slowly updated withthe common frequency error estimate. The feedback based frequencytracking loop for each finger processor is initialized with thefrequency error estimate for that finger processor and enabled (block1316). The frequency tracking loop for each finger processor thereaftercontinually estimates the phase of the pilot symbols and updates thefrequency error estimate for that finger processor.

For time tracking, QTT is performed to obtain a timing error estimatefor each finger processor (block 1322). The time tracking loop for eachfinger processor is initialized with the timing error estimate andenabled (block 1324). The time tracking loop thereafter continuallyestimates the timing of the pilot symbols and updates the timing errorestimate. QTT may be performed in parallel with QFT to reduce the awakeduration, as indicated by the two paths for frequency and time trackingin FIG. 13.

After blocks 1316 and 1324, for each finger processor, the rotator isoperated based on the output from the frequency tracking loop, and thesampling unit is operated based on the output from the time trackingloop, as shown in FIG. 6. Detection of the paging indicator is performedwith the frequency and time tracking loops running in each fingerprocessor and using NCP (block 1330). Prior to going to sleep, thelatest values of the common frequency error estimate are saved (block1332). The amount of time required to perform frequency and timetracking in the next awake interval is determined based on the expectedchannel conditions (block 1334). The timer is set appropriately, and thewireless device goes to sleep until the timer expires.

Detection performance with NCP was evaluated and compared againstdetection performance with a causal infinite impulse response (IIR)filter. It can be shown that NCP improves detection performance forcertain operating scenarios including high speed. Detection performanceis also more resilient to frequency error with NCP, which caneffectively deal with a potentially large residual frequency error fromQFT. The resiliency to frequency error may also be exploited to reducethe amount of time allocated for frequency tracking or to possiblyeliminate frequency tracking prior to performing detection.

QFT, QTT, and NCP may be used by a wireless device to reduce RF awaketime per awake interval during DRX operation in the idle mode. QFT, QTT,and NCP take less time to perform and provide better performance thanconventional schemes for frequency tracking, time tracking, and pilotfiltering, respectively. A key advantage of QFT, QTT, and NCP is reducedbattery power consumption and extended battery standby time. Otheradvantages from using NCP include improved detection performance underhigh frequency dynamics and flexibility to perform frequency trackingafter (instead of before) paging indicator detection.

For clarity, specific embodiments of QFT, QTT, and NCP have beendescribed above. QFT, QTT, and NCP may also be performed in othermanners, and this is within the scope of the invention. For example,QFT, QTT, and NCP may be performed based on descrambled samples insteadof pilot symbols. In this case, coherent accumulation and non-coherentaccumulation are performed on samples. Any one, any combination, or allthree techniques may be used for PICH detection.

For clarity, QFT, QTT, and NCP have been specifically described fordetection of paging indicators in W-CDMA. In general, these techniquesmay be used for detection of various types of signaling such asindicators, bits, symbols, acknowledgments, requests, and so on. Thesetechniques may be used for W-CDMA and other wireless communicationsystems.

FIG. 14 shows a process 1400 for performing QFT for receivingsporadically transmitted signaling (e.g., paging indicators) in awireless communication system. Initially, the wireless device wakes upfrom sleep to receive signaling during DRX operation (block 1412).Multiple hypothesized frequency errors are applied to an input signal(e.g., pilot symbols or descrambled samples) to obtain multiple rotatedsignals (block 1414). The energies of the rotated signals aredetermined, e.g., by performing coherent accumulation followed by energycomputation (block 1416). A frequency error estimate is determined basedon the energies of the rotated signals (block 1418) and used fordetection of the signaling (block 1420).

FIG. 15 shows a process 1500 for performing QTT for receivingsporadically transmitted signaling in the wireless communication system.Initially, the wireless device wakes up from sleep to receive signaling(block 1512). Coherent accumulation is performed on the input signal fora first set of time offsets (e.g., early, on-time, and late) (block1514). Interpolation may be performed on the outputs of the coherentaccumulation for the first set of time offsets to obtain intermediatevalues for a second set of time offsets (e.g., at chip×8 resolution)(block 1516). The energies of the intermediate values may be computed(block 1518), and non-coherent accumulation may be performed on theenergies of the intermediate values for the second set of time offsets(block 1520). A timing error estimate is derived based on the outputs ofthe non-coherent accumulation (block 1522) and used for detection of thesignaling (block 1524).

FIG. 16 shows a process 1600 for performing NCP for receivingsporadically transmitted signaling in the wireless communication system.Initially, the wireless device wakes up from sleep to receive signaling(block 1612). Pilot symbols are filtered with a non-causal filter toobtain pilot estimates for one antenna for non-STTD and for two antennasfor STTD (block 1614). Detection of the signaling is then performedbased on the pilot estimates, as described above (block 1616).

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, software, or acombination thereof. For a hardware implementation, the processing unitsused to perform any one, any combination, or all of the techniques(e.g., pilot filter 620 in FIG. 6, QFT units 638 a in FIG. 8A, QFT unit638 b in FIG. 8B, QTT unit 634 a in FIG. 10, and so on) may beimplemented within one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, micro-controllers,microprocessors, electronic devices, other electronic units designed toperform the functions described herein, or a combination thereof.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory unit 572 in FIG. 5) and executed by aprocessor (e.g., controller 570). The memory unit may be implementedwithin the processor or external to the processor.

Headings are included herein for reference and to aid in locatingcertain sections. These headings are not intended to limit the scope ofthe concepts described therein under, and these concepts may haveapplicability in other sections throughout the entire specification.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. An apparatus comprising: a controller operative to wake up from sleepto receive signaling during discontinuous reception (DRX) operation; aprocessor operative to apply a plurality of hypothesized frequencyerrors to an input signal to obtain a plurality of rotated signals, todetermine energies of the plurality of rotated signals, and to determinea frequency error estimate based on the energies of the plurality ofrotated signals; and a demodulator operative to use the frequency errorestimate for detection of the signaling.
 2. The apparatus of claim 1,wherein the processor is operative to accumulate each rotated signalover a predetermined period to obtain an accumulated value for therotated signal and to compute energy of the accumulated value.
 3. Theapparatus of claim 2, wherein the controller is operative to select thepredetermined period based on expected channel conditions.
 4. Theapparatus of claim 1, wherein the processor is operative to identify alargest energy among the energies of the plurality of rotated signalsand to provide a hypothesized frequency error corresponding to thelargest energy as the frequency error estimate.
 5. The apparatus ofclaim 1, wherein the controller is operative to distribute the pluralityof hypothesized frequency errors uniformly over a range of possiblefrequency errors.
 6. The apparatus of claim 1, wherein the controller isoperative to distribute the plurality of hypothesized frequency errorsnon-uniformly over a range of possible frequency errors and to usesmaller frequency error spacing for at least one subrange of frequencyerrors with higher likelihood of containing an actual frequency error.7. The apparatus of claim 1, wherein the controller is operative todetermine a range of possible frequency errors based on expected channelconditions and to select the plurality of hypothesized frequency errorsbased on the range of possible frequency errors.
 8. The apparatus ofclaim 1, wherein the demodulator is operative to perform detection for apaging indicator sent at predetermined time interval.
 9. The apparatusof claim 1, wherein the processor is operative to receive pilot symbolsfor the input signal.
 10. The apparatus of claim 1, wherein theprocessor is operative to receive descrambled samples for the inputsignal.
 11. A method comprising: waking up from sleep to receivesignaling during discontinuous reception (DRX) operation; applying aplurality of hypothesized frequency errors to an input signal to obtaina plurality of rotated signals; determining energies of the plurality ofrotated signals; determining a frequency error estimate based on theenergies of the plurality of rotated signals; and using the frequencyerror estimate for detection of the signaling.
 12. The method of claim11, wherein the determining the energies of the plurality of rotatedsignals comprises accumulating each rotated signal over a predeterminedperiod to obtain an accumulated value for the rotated signal, andcomputing energy of the accumulated value for each rotated signal. 13.The method of claim 11, wherein the determining the frequency errorestimate comprises identifying a largest energy among the energies ofthe plurality of rotated signals, and providing a hypothesized frequencyerror corresponding to the largest energy as the frequency errorestimate.
 14. The method of claim 11, further comprising: performingdetection for a paging indicator sent at a predetermined time interval.15. An apparatus comprising: means for waking up from sleep to receivesignaling during discontinuous reception (DRX) operation; means forapplying a plurality of hypothesized frequency errors to an input signalto obtain a plurality of rotated signals; means for determining energiesof the plurality of rotated signals; means for determining a frequencyerror estimate based on the energies of the plurality of rotatedsignals; and means for using the frequency error estimate for detectionof the signaling.
 16. The apparatus of claim 15, wherein the means fordetermining the energies of the plurality of rotated signals comprisesmeans for accumulating each rotated signal over a predetermined periodto obtain an accumulated value for the rotated signal, and means forcomputing energy of the accumulated value for each rotated signal. 17.The apparatus of claim 15, wherein the means for determining thefrequency error estimate comprises means for identifying a largestenergy among the energies of the plurality of rotated signals, and meansfor providing a hypothesized frequency error corresponding to thelargest energy as the frequency error estimate.
 18. A method comprising:applying a plurality of hypothesized frequency errors to an input signalto obtain a plurality of rotated signals; determining energies of theplurality of rotated signals for a first transmit antenna; determiningenergies of the plurality of rotated signals for a second transmitantenna; determining overall energies of the plurality of rotatedsignals for the first and second antennas; and determining a frequencyerror estimate based on the overall energies of the plurality of rotatedsignals.
 19. The method of claim 18, further comprising: accumulatingthe plurality of rotated signals separately over a predetermined periodto obtain a first plurality of accumulated values used to determine theenergies of the plurality of rotated signals for the first transmitantenna; scaling the plurality of rotated signals with a scalingsequence for the second transmit antenna to obtain a plurality of scaledsignals; and accumulating the plurality of scaled signals separatelyover the predetermined period to obtain a second plurality ofintermediate values used to determine the energies of the plurality ofrotated signals for the second transmit antenna.
 20. The method of claim19, wherein the determining the frequency error estimate comprisesidentifying a largest overall energy among the overall energies of theplurality of rotated signals, and providing a hypothesized frequencyerror corresponding to the largest overall energy as the frequency errorestimate.
 21. An apparatus comprising: a controller operative to wake upfrom sleep to receive signaling during discontinuous reception (DRX)operation; a processor operative to perform coherent accumulation on aninput signal for a first plurality of time offsets, to performinterpolation from the first plurality of time offsets to a secondplurality of time offsets, and to perform non-coherent accumulationafter the interpolation to obtain a timing error estimate; and ademodulator operative to use the timing error estimate for detection ofthe signaling.
 22. The apparatus of claim 21, wherein the processor isoperative to perform linear interpolation on outputs of the coherentaccumulation for the first plurality of time offsets to obtainintermediate values for a second plurality of time offsets and toperform non-coherent accumulation based on the intermediate values. 23.The apparatus of claim 22, wherein the processor is operative to computeenergies of the intermediate values for the second plurality of timeoffsets and to perform non-coherent accumulation based on the energiesof the intermediate values for the second plurality of time offsets. 24.The apparatus of claim 23, wherein the processor is operative toidentify a largest energy among non-coherently accumulated energies forthe second plurality of time offsets and to provide a time offsetcorresponding to the largest energy as the timing error estimate. 25.The apparatus of claim 21, wherein the processor is operative to performparabolic interpolation on outputs of the non-coherent accumulation forthe first plurality of time offsets.
 26. The apparatus of claim 21,wherein the controller is operative to select length of the coherentaccumulation and length of the non-coherent accumulation based onexpected channel conditions.
 27. The apparatus of claim 21, wherein theprocessor is operative to receive symbols at two times chip rate and toprovide the timing error estimate with a resolution of one eighth chipperiod or better.
 28. A method comprising: waking up from sleep toreceive signaling during discontinuous reception (DRX) operation;performing coherent accumulation on an input signal for a firstplurality of time offsets; performing interpolation from the firstplurality of time offsets to a second plurality of time offsets;performing non-coherent accumulation after the interpolation; deriving atiming error estimate based on outputs of the non-coherent accumulation;and using the timing error estimate for detection of the signaling. 29.The method of claim 28, wherein the performing interpolation on thefirst plurality of time offsets comprises performing linearinterpolation on outputs of the coherent accumulation for the firstplurality of time offsets to obtain intermediate values for a secondplurality of time offsets, and wherein the non-coherent accumulation isperformed based on the intermediate values.
 30. The method of claim 29,further comprising: computing energies of the intermediate values forthe second plurality of time offsets, and wherein the non-coherentaccumulation is performed based on the energies of the intermediatevalues for the second plurality of time offsets.
 31. The method of claim30, further comprising: identifying a largest energy amongnon-coherently accumulated energies for the second plurality of timeoffsets; and providing a time offset corresponding to the largest energyas the timing error estimate.
 32. The method of claim 28, wherein theperforming interpolation on the first plurality of time offsetscomprises performing parabolic interpolation on outputs of thenon-coherent accumulation for the first plurality of time offsets. 33.An apparatus comprising: means for waking up from sleep to receivesignaling during discontinuous reception (DRX) operation; means forperforming coherent accumulation on an input signal for a firstplurality of time offsets; means for performing interpolation from thefirst plurality of time offsets to a second plurality of time offsets;means for performing non-coherent accumulation after the interpolation;means for deriving a timing error estimate based on outputs of thenon-coherent accumulation; and means for using the timing error estimatefor detection of the signaling.
 34. The apparatus of claim 33, whereinthe means for performing interpolation on the first plurality of timeoffsets comprises means for performing linear interpolation on outputsof the coherent accumulation for the first plurality of time offsets toobtain intermediate values for a second plurality of time offsets. 35.The apparatus of claim 34, further comprising: means for computingenergies of the intermediate values for the second plurality of timeoffsets, and wherein the non-coherent accumulation is performed based onthe energies of the intermediate values for the second plurality of timeoffsets; means for identifying a largest energy among non-coherentlyaccumulated energies for the second plurality of time offsets; and meansfor providing a time offset corresponding to the largest energy as thetiming error estimate.
 36. A method comprising: performing coherentaccumulation on an input signal for a first transmit antenna at a firstplurality of time offsets; performing coherent accumulation on the inputsignal for a second transmit antenna at the first plurality of timeoffsets; performing interpolation from the first plurality of timeoffsets to a second plurality of time offsets for each of the first andsecond transmit antennas; determining energies for the second pluralityof time offsets for each of the first and second transmit antennas;combining the energies for the first and second transmit antennas foreach of the second plurality of time offsets; performing non-coherentaccumulation of the energies for the second plurality of time offsets;and obtaining a timing error estimate based on outputs of thenon-coherent accumulation.
 37. The method of claim 36, wherein theperforming interpolation comprises performing linear interpolation onoutputs of the coherent accumulation for the first transmit antenna toobtain intermediate values at a second plurality of time offsets for thefirst transmit antenna, and performing linear interpolation on outputsof the coherent accumulation for the second transmit antenna to obtainintermediate values at the second plurality of time offsets for thesecond transmit antenna.
 38. The method of claim 36, further comprising:identifying a largest energy among non-coherently accumulated energiesfor the second plurality of time offsets; and providing a time offsetcorresponding to the largest energy as the timing error estimate.
 39. Anapparatus comprising: a controller operative to wake up from sleep toreceive signaling during discontinuous reception (DRX) operation; and ademodulator operative to filter pilot symbols with a non-causal filterto obtain pilot estimates and to perform detection for the signalingbased on the pilot estimates.
 40. The apparatus of claim 39, wherein thedemodulator is operative to filter the pilot symbols with a non-causalfinite impulse response (FIR) filter having equal number of taps on bothsides of each signaling symbol to be detected.
 41. The apparatus ofclaim 39, wherein the demodulator is operative to derive at least onechannel gain estimate for at least one signaling symbol based on thepilot estimates, to multiply the at least one signaling symbol with theat least one channel gain estimate to obtain at least one demodulatedsymbol, and to sum inphase and quadrature components of the at least onedemodulated symbol to obtain a detected value for the signaling.
 42. Amethod comprising: waking up from sleep to receive signaling duringdiscontinuous reception (DRX) operation; filtering pilot symbols with anon-causal filter to obtain pilot estimates; and performing detectionfor the signaling based on the pilot estimates.
 43. The method of claim42, wherein the filtering the pilot symbols comprises filtering thepilot symbols with a non-causal finite impulse response (FIR) filterhaving equal number of taps on both sides of each signaling symbol to bedetected.
 44. The method of claim 42, wherein the performing detectioncomprises deriving at least one channel gain estimate for at least onesignaling symbol based on the pilot estimates, multiplying the at leastone signaling symbol with the at least one channel gain estimate toobtain at least one demodulated symbol, and summing inphase andquadrature components of the at least one demodulated symbol to obtain adetected value for the signaling.
 45. A method comprising: filtering afirst set of pilot symbols with a first non-causal filter for a firstantenna to obtain a first set of at least one pilot estimate for thefirst antenna; filtering a second set of pilot symbols with a secondnon-causal filter for a second antenna to obtain a second set of atleast one pilot estimate for the second antenna; and performingdetection of signaling based on the first and second sets of at leastone pilot estimate.
 46. The method of claim 45, further comprising:selecting the first set of pilot symbols to include equal number of sumand difference pilot symbols; and selecting the second set of pilotsymbols to include equal number of sum and difference pilot symbols. 47.The method of claim 45, wherein the performing detection of thesignaling comprises performing space-time transmit diversity (STTD)decoding of at least one pair of signaling symbols with the first andsecond sets of at least one pilot estimate to obtain a detected valuefor the signaling.
 48. The method of claim 45, wherein the first set ofpilot symbols is equal to the second set of pilot symbols.
 49. Themethod of claim 45, wherein the first set of pilot symbols isnon-symmetric with the signaling and includes unequal numbers of pilotsymbols on left and right sides of the signaling.
 50. The method ofclaim 45, wherein the second set of pilot symbols includes at least onepilot symbol not included in the first set of pilot symbols.
 51. Themethod of claim 50, further comprising: filtering the first set of pilotsymbols with a third non-causal filter for the second antenna to obtaina third set of at least one pilot estimate for the second antenna; andfiltering the second set of pilot symbols with a fourth non-causalfilter for the first antenna to obtain a fourth set of at least onepilot estimate for the first antenna, and wherein the detection of thesignaling is performed further based on the third and fourth sets of atleast one pilot estimate.
 52. The method of claim 51, furthercomprising: performing space-time transmit diversity (STTD) decoding ofat least one pair of signaling symbols with the first, second, third,and fourth sets of at least one pilot estimate to obtain a detectedvalue for the signaling.
 53. The method of claim 51, further comprising:averaging the first and fourth sets of at least one pilot estimate forthe first antenna to obtain a first set of at least one averaged pilotestimate for the first antenna; averaging the second and third sets ofat least one pilot estimate for the second antenna to obtain a secondset of at least one averaged pilot estimate for the second antenna; andperforming space-time transmit diversity (STTD) decoding of at least onepair of signaling symbols with the first and second sets of at least oneaveraged pilot estimate to obtain a detected value for the signaling.54. An apparatus comprising: a processor operative to perform quickfrequency tracking to obtain at least one frequency error estimate forat least one finger processor and to perform quick time tracking toobtain at least one timing error estimate for the at least one fingerprocessor; and a demodulator operative to perform detection forsignaling with the at least one frequency error estimate and the atleast one timing error estimate for the at least one finger processor.55. The apparatus of claim 54, wherein the processor is operative, foreach finger processor, to perform coherent accumulation to obtainenergies for a plurality of hypothesized frequency errors and todetermine a frequency error estimate for the finger processor based onthe energies for the plurality of hypothesized frequency errors.
 56. Theapparatus of claim 54, wherein the processor is operative, for eachfinger processor, to perform coherent accumulation, interpolation, andnon-coherent accumulation to obtain energies for a plurality of timeoffsets and to determine a timing error estimate for the fingerprocessor based on the energies for the plurality of time offsets. 57.The apparatus of claim 54, wherein the demodulator is operative tofilter pilot symbols with a non-causal filter to obtain pilot estimatesand to perform detection for the signaling based on the pilot estimates.58. The apparatus of claim 54, wherein the processor is operative toperform quick frequency tracking and quick time tracking in parallel.59. The apparatus of claim 54, wherein the controller is operative todetermine an amount of time to perform quick frequency tracking andquick time tracking in a next awake interval based on expected channelconditions and to determine a sleep duration based on the amount of timeto perform quick frequency tracking and quick time tracking in the nextawake interval.
 60. The apparatus of claim 54, wherein the processor isoperative to perform detection for a paging indicator sent at apredetermined time interval.
 61. A method comprising: performing quickfrequency tracking to obtain at least one frequency error estimate forat least one finger processor; performing quick time tracking to obtainat least one timing error estimate for the at least one fingerprocessor; and performing detection of signaling with the at least onefrequency error estimate and the at least one timing error estimate forthe at least one finger processor.
 62. The method of claim 61, whereinthe performing quick frequency tracking comprises, for each fingerprocessor, performing coherent accumulation to obtain energies for aplurality of hypothesized frequency errors, and determining a frequencyerror estimate for the finger processor based on the energies for theplurality of hypothesized frequency errors.
 63. The method of claim 61,wherein the performing quick time tracking comprises, for each fingerprocessor, performing coherent accumulation, interpolation, andnon-coherent accumulation to obtain energies for a plurality of timeoffsets, and determining a timing error estimate for the fingerprocessor based on the energies for the plurality of time offsets. 64.The method of claim 61, further comprising: filtering pilot symbols witha non-causal filter to obtain pilot estimates, and wherein the detectionof the signaling is performed based on the pilot estimates.
 65. Themethod of claim 61, further comprising: determining an amount of time toperform quick frequency tracking and quick time tracking in a next awakeinterval based on expected channel conditions; and determining a sleepduration based on the amount of time to perform quick frequency trackingand quick time tracking in the next awake interval.
 66. An apparatuscomprising: means for performing quick frequency tracking to obtain atleast one frequency error estimate for at least one finger processor;means for performing quick time tracking to obtain at least one timingerror estimate for the at least one finger processor; and means forperforming detection of signaling with the at least one frequency errorestimate and the at least one timing error estimate for the at least onefinger processor.
 67. The apparatus of claim 66, wherein the means forperforming quick frequency tracking comprises, for each fingerprocessor, means for performing coherent accumulation to obtain energiesfor a plurality of hypothesized frequency errors, and means fordetermining a frequency error estimate for the finger processor based onthe energies for the plurality of hypothesized frequency errors.
 68. Theapparatus of claim 66, wherein the means for performing quick timetracking comprises, for each finger processor, means for performingcoherent accumulation, interpolation, and non-coherent accumulation toobtain energies for a plurality of time offsets, and means fordetermining a timing error estimate for the finger processor based onthe energies for the plurality of time offsets.
 69. The apparatus ofclaim 66, further comprising: means for filtering pilot symbols with anon-causal filter to obtain pilot estimates, and wherein the detectionof the signaling is performed based on the pilot estimates.